System and method for non-sinusoidal current waveform excitation of electrical generators

Abstract

An electrical generator includes a stator having fractional-slot concentrated windings and a rotor having field windings. A drive is provided having a circuit to control current flow to the field windings and a controller to input an initial DC field current demand to the circuit to cause the circuit to output an initial DC field current representative of a DC field current demand that would cause an electrical generator having sinusoidal stator windings to output a desired AC power. The controller receives feedback on the magnetic field generated by the initial DC field current, isolates an ideal fundamental component of the magnetic field based on the feedback and to generate a modified DC field current demand, and inputs the modified DC field current demand to the circuit, thereby causing the circuit to output an instantaneous non-sinusoidal current to the field windings to generate a sinusoidal rotating air gap magnetic field.

What is claimed is: 
     
       1. An electrical generator comprising:
 a stator including a plurality of fractional-slot concentrated windings; 
 a rotor positioned within the stator and configured to rotate relative thereto, the rotor having field windings electrically coupled thereto configured to generate a rotating magnetic field in an air gap between the stator and the rotor responsive to a current applied thereto; and 
 a drive having an input connectable to a power source and an output connectable to the field windings, the drive comprising:
 a circuit configured to control current flow to the field windings; and 
 a controller connected to the circuit and programmed to:
 input an initial DC field current demand signal to the circuit to cause the circuit to output an initial DC field current; 
 receive feedback on the rotating magnetic field generated by the initial DC field current; 
 generate a modified DC field current demand signal based on the received feedback; and 
 input the modified DC field current demand signal to the circuit to cause the circuit to output a desired DC current waveform. 
 
 
 
     
     
       2. The electrical generator of  claim 1  wherein the controller is further programmed to:
 apply an adjustment factor to the initial DC field current to modify an amplitude thereof; 
 determine and isolate an instantaneous fundamental component of the rotating magnetic field based on the feedback; 
 generate an ideal fundamental component based on the isolated instantaneous fundamental component; and 
 remove the adjustment factor upon generation of the ideal fundamental component. 
 
     
     
       3. The electrical generator of  claim 2  wherein the controller is further programmed to perform a Laplace transfer function of the rotating magnetic field, the Laplace transfer function of the rotating magnetic field derived from the initial DC field current and the ideal fundamental component of the rotating magnetic field. 
     
     
       4. The electrical generator of  claim 2  wherein the controller is further programmed to:
 determine instantaneous harmonic components of the rotating magnetic field; 
 eliminate the instantaneous harmonic components of the rotating magnetic field feedback to isolate the instantaneous fundamental component; and 
 generate the ideal fundamental component from a lookup table based on the isolated instantaneous fundamental component. 
 
     
     
       5. The electrical generator of  claim 4  wherein the controller is further programmed to perform a fast Fourier transform (FFT) on the rotating magnetic field feedback to determine the instantaneous fundamental component and instantaneous harmonic components. 
     
     
       6. The electrical generator of  claim 4  wherein the controller is further programmed to:
 access the lookup table having stored therein ideal fundamental components of a rotating magnetic field associated with each of a plurality of DC field current demand signals, the ideal fundamental components comprising a highest fundamental component for each of the plurality of DC field current demand signals; 
 compare the isolated instantaneous fundamental component associated with the initial DC field current demand signal with the ideal fundamental components associated with the initial DC field current demand signal in the lookup table; and 
 generate the ideal fundamental component based on the comparison. 
 
     
     
       7. The electrical generator of  claim 1  wherein the controller is further programmed to adjust a timing of an input current from the power source, as compared to a timing of the initial DC field current, according to the modified DC field current demand signal to produce a non-sinusoidal current output from the circuit. 
     
     
       8. The electrical generator of  claim 1  wherein the circuit comprises one of an inverter configured to provide for variable speed operation of the electrical generator and a dedicated circuit configured to provide for fixed speed operation of the electrical generator, such that the electrical generator functions as an alternator. 
     
     
       9. The electrical generator of  claim 1  wherein the initial DC field current demand is representative of a DC field current demand that would cause an electrical generator having sinusoidal stator windings to output a desired AC power. 
     
     
       10. An electrical generator comprising:
 a stator including a plurality of non-sinusoidal concentrated windings; 
 a rotor positioned within the stator and configured to rotate relative thereto, the rotor having field windings configured to generate a rotating magnetic field in an air gap between the stator and the rotor responsive to a current applied thereto; 
 a drive to control current flow from a power source to the field windings, the drive configured to:
 provide an initial input current to the rotor based on a first current demand; 
 receive feedback on the rotating magnetic field generated by the initial input current; 
 generate a second current demand based on the feedback; and 
 provide an instantaneous modified input current to the field windings based on the second current demand so as to generate a sinusoidal rotating magnetic field in the air gap and generate AC power in the electrical generator, wherein the instantaneous modified input current comprises a non-sinusoidal current waveform. 
 
 
     
     
       11. The electrical generator of  claim 10  wherein the drive is further configured to:
 determine an instantaneous fundamental component and instantaneous harmonic components of the rotating magnetic field using a fast Fourier transform (FFT); 
 apply a correction to the instantaneous fundamental component of the rotating magnetic field to generate an ideal fundamental component; and 
 generate the second current demand based on the ideal fundamental component. 
 
     
     
       12. The electrical generator of  claim 10  wherein the drive is further configured to access a database having stored thereon each of a plurality of input current demands representative of DC field current demands and ideal fundamental components of a rotating magnetic field generated from each of the plurality of input current demands, each ideal fundamental component representing a highest fundamental component resulting from input of an input current demand to an electrical generator having sinusoidal windings. 
     
     
       13. The electrical generator of  claim 10  wherein the drive is further configured to determine a modified input current needed to generate the ideal fundamental component of the air rotating magnetic field. 
     
     
       14. The electrical generator of  claim 13  wherein the drive is further configured to:
 zero the initial input current; and 
 adjust a timing of a current flow from the power source according to the second current demand so as to produce the non-sinusoidal current waveform of the modified input current. 
 
     
     
       15. The electrical generator of  claim 10  wherein the first current demand is representative of a DC field current demand that would cause an electrical generator having sinusoidal stator windings to output a desired AC power.